INFXTS0R1A.L ANIMALCULES. 59 



to be siliceous, uot calcareous, — but tliis dili'erence, it would seem, 

 is questionable. 



Mr. Carter, of Boinl)ay, in an able paper on the fresbwater 

 sponges, (Transactions of the Medical and Physical Society of 

 Bombay, 1847, Appendix.) points out the close resemblance between 

 the separated indi^n duals, or Proteans, to the members of the genus 

 Amoeba of Ehrenberg, and concludes \\'ith the remark : — " Thus 

 does every step toAvards the ultimate stnictm-e of the freshwater 

 sponge, every form that is taken bj- the living matter of which it is 

 composed, appear still more nearly to approximate it to the nature 

 of the genera of Ehrenberg's Pseudopoda.''' 



The next group in advance is characterized by its members ha-ving 

 mouths, and which are known to Siebold as Stomatoda. The affini- 

 ties of these animals vary in the case of different families. For 

 although the Polygastrica, by their general peculiarities, are separable 

 from all other classes of animals, yet their several families have — 

 setting aside their disputed polygastric stinicture, hardly any features 

 in common, save their smallness, their habitat, and theii' simple 

 organization, with, what is important, their propagation by spon- 

 taneous fission, and, in almost every case, their want of sjTnmetry. 

 Their general conformation, as seen by the plates, is most varied, as 

 also is their manifestation of life. Some, as the Vorticellina, are 

 fixed by a stem to a foreign object, and in many points resemble 

 Polypes, with which indeed they have been classed ; and their 

 resemblance is the greater, where the stem is branched and rigid, to 

 Sertularian Polypes. 



In its mode of progression, the Colejjs recalls that of the Daphmce, 

 but all similarity of organization is wanting. The Euplotes monostylm 

 presents several characters belonging to the Rotatoria, but is asym- 

 metrical, has no such alimentary canal as the latter, and propagates 

 by fission. 



Some anomalous forms, such as Bicti/ocTia, although, by reason of 

 their siliceous composition, and peculiar conformation, reckoned among 

 the Polyga.striea by Ehrenberg, would appear to approximate nearer 

 to the Phytolitharia than to any other class. The siliceous shelled 

 Polygastrica have an affinity also with a class of animals newly dis- 

 covered and brought together by the indefatigable Prof. Ehrenberg, 



